Duncan Miller

A few years ago, faceting friends of mine in Durban bought some green gem quality material sold as epidote or possibly peridot. It was nice clear green, and some pieces of rough still adhered to a matrix, "dug out of the ground right in front" of the vendor from Moçambique. The cutting and polishing was easy, apparently working like tanzanite. But the surface of the polished stone degraded quite rapidly, developing hazy spots, so samples were sent to me for identification.

The specific gravity measured by hydrostatic weighing was 3,55. It was quite soft, with a Mohs’s hardness of about 5, and had perfect cleavage, forming faces at 90° to each other. This indicated that it probably was cubic, so it could not be epidote, or peridot. Between crossed polars it was isotropic, which figured with its being cubic, but the cleavage meant it wasn’t glass. Under magnification, it contained swarms of fine, round bubbles. This was a puzzle. So I polished a face to measure the refractive index, which was 1,73.

This combination of properties indicated synthetic periclase (MgO). Webster’s Gems notes that it has been marketed under the trade name of Lavernite. So what about the matrix specimen? A closer look at that showed some nice little brown cubic crystals lining vugs in cleaved green masses. Another piece had an opaque, vesicular brown matrix, probably also periclase but with higher iron content. The vendor had lied.

A piece of synthetic periclase (MgO) sold as natural faceting rough. The front and side faces are cleavage faces at 90° to each other. The top face is a saw cut. The sample is 15 mm long.


A ‘matrix’ specimen of synthetic periclase, with small brown cubic crystals lining vugs in the green periclase ‘matrix’. The field of view is 25 mm wide.